1. Field of the Invention
The present invention relates to a toner suitable for electrophotography, electrostatic recording, electrostatic printing and the like, to a producing method for the same, and to an image-forming method using the toner.
2. Description of the Related Art
Image forming based on electrophotography generally involves a series of the following individual steps: a latent electrostatic image-forming step in which using a variety of means a latent electrostatic image is formed on a photoconductor (hereinafter referred to as a latent electrostatic image bearing member, an image bearing member, and an electrophotographic photoconductor); a developing step in which the formed latent electrostatic image is developed by application of a toner to form a toner image; a transferring step in which the toner image is transferred to a recording member such as a paper; a fixing step in which the toner image transferred to the recording member is fixed thereto by applying heat, pressure, heat and pressure, or vapor of a solvent; and a cleaning step in which toner particles remained on the photoconductor are removed, for example.
It is required that toners for electrophotography be produced by more energy-saving, environment friendly processes. The conventional method of pulverization is employed in the method for producing the toner. However, in recent years, media-based chemical methods such as an emulsion aggregation method, a suspension polymerization method, an emulsion dispersion method, a dissolution and suspension method, and a dissolution, suspension and extension method have been used in most cases for producing the toners.
In the suspension polymerization method, toner materials containing monomers, a polymerization initiator and the like are dispersed in an aqueous medium to form oil droplets, followed by heat treatment to cause a polymerization reaction to take place for producing the toner.
In the emulsion dispersion method, toner materials containing polymers and the like are mixed with an aqueous medium to form oil droplets by allowing the toner materials to be dispersed or emulsified in or with the aqueous medium for producing the toner (see Japanese Patent Application Laid-Open (JP-A) No. 05-66600 and 08-211655). The dissolution and suspension method consists of the suspension preparing step in which an oil component produced by adding a binder resin in an organic solvent in which the binder resin is resolvable is suspended in an aqueous component to be particulate, and the step of removing the organic solvent from the suspension (see Japanese Patent (JP-B) No. 3141783).
In view of recent environmental problems, as chemical toners produced through these chemical methods, chemical toners such as capsule toner, core shell toner, etc. are available, and such toners have a form that enables efficient provision of desired functions.
In such methods for producing toners, which use the pulverization method, how uniformly each constituent material is dispersed and pulverized is important to ensure that the resultant toner particles have uniform shapes. In general, toner particles have amorphous shapes with randomly-sized cross sections, and control of the shape or structure of toner particles become very difficult. Moreover, when a large amount of coloring agents, releasing agents, charge-controlling agents and the like are added to the toner, these additives tend to migrate to the surfaces of toner particles during a pulverization process because they cleavage along the crystal plane of the additives, resulting in a problem that toner characteristics such as flowability and charging properties may be reduced, e.g., variations may occur in the charging properties among individual toner particles.
The methods for producing toners which involve chemical methods can produce toner particles that have smaller diameters and a narrower particle size distribution than those produced by the method for producing the toners involving the pulverization method. However, the toner surface becomes hydrophilic because toner is produced either in water or hydrophilic medium, and then the charging properties of toner particles reduce, the temporal stability and environmental characteristics become unstable. This may cause such problems as abnormal development and transfer operations, toner scatterings, or poor image quality. Moreover, the methods for producing the toner which involve chemical methods entail generation of a large amount of waste solution and require a large amount of energy for drying of produced toner particles. This is not preferred in terms of environmental impact. Therefore, the methods for producing a toner using a supercritical fluid have been developed.
As a method for producing a toner using a supercritical fluid, for example, Japanese Patent Application Laid-Open (JP-A) No. 2001-312098 proposes a method for producing toner particles using RESS (Rapid Expansion of Supercritical Solutions) technique. This technique, however, is applicable to only resin that can be dissolved in supercritical fluids, and provides a narrow range of choice of applicable resins. For example, the solubilities of high-molecular mass ingredients or gels (called H body) needed in the toner are of extremely low solubility. In addition, a supercritical fluid, for example, inexpensive and potent styrene-acrylic resins and polyester resins that are generally used in the toner field are also of extremely low solubility. Thus, there is a problem that they cannot be used as they are.
To solve the foregoing problems Japanese Patent Application Laid-Open (JP-A) Nos. 2004-161824, 2004-144778 and 2005-107405 propose a technique in which rather than dissolving resin in a supercritical fluid, colored resin that has been previously melted and kneaded is granulated by application of shearing force using a dispersing agent in a insoluble condition. This technology has a problem that it broadens the particle size distribution, though a wide range is ensured for the choice of materials. In particular, broader particle distributions are a critical drawback for obtaining high-resolution images as required by recent toners.
No method for producing a toner has been provided that ensures a sharp particle size distribution and excellent toner characteristics such as charging properties, environmental impact, and temporal stability, creates little waste solution, produces toner containing no monomers left over, requires no drying process and is low cost. Likewise, neither a toner produced by this method for producing the toner nor an image-forming apparatus using the toner has been provided.